black mallee vs black gum

black mallee and black gum both are nouns.

Word	Noun	Adjective	Verb	Adverb
black mallee	Yes	No	No	No
black gum	Yes	No	No	No

As nouns, black mallee and black gum are synonyms defined as:

black mallee and black gum: a small mallee with rough dark-colored bark toward the butt; yields a red eucalyptus kino gum

Other synonyms of black mallee include black sally, Eucalytus stellulata.

black mallee (noun)	black gum (noun)
a small mallee with rough dark-colored bark toward the butt; yields a red eucalyptus kino gum	columnar tree of eastern North America having horizontal limbs and small leaves that emerge late in spring and have brilliant color in early fall
	a small mallee with rough dark-colored bark toward the butt; yields a red eucalyptus kino gum